Valve mechanism for an internal combustion engine

ABSTRACT

Valve mechanism in an internal combustion engine, comprising at least one intake valve and at least one exhaust valve in each cylinder. For each cylinder there are at least two rocker arms journalled on a rocker arm shaft for operating a respective one of the valves. A transmission (15,17,18) selectively moves the exhaust valve (5) from a closed position toward an open position during the engine intake stroke to draw exhaust into the cylinder (30) during the intake stroke.

The present invention relates to a valve mechanism in an internalcombustion engine, comprising at least one intake valve and at least oneexhaust valve in each cylinder and, for each cylinder, at least tworocker arms journalled on a rocker arm shaft for operating the valves.

There are great potential gains to be achieved by reducing the harmfulsubstances in diesel exhaust by recirculation of exhaust, withoutadversely affecting engine efficiency or soot level as much as withother methods.

Recycling exhaust which has first been cooled is an effective step,especially at high load, but the required cooling power will be quitehigh and a cooling device will be required which can provide half thecooling power of the engine intercooler. Since the exhaust is pollutedand hot, there will, however, be practical problems with such a system.Returning exhaust without cooling has positive effects primarily whenengine load is low but not quite as positive when the engine load ishigh.

Conventional systems for exhaust return comprise shutter and valvedevices in the exhaust and intake systems. When using such systems inturbo-charged engines, there will, however, be problems due to the factthat the pressure is higher on the intake side than on the exhaust side.Thus, some form of pump device is needed to get the exhaust to thepressure side of the turbo compressor. Alternatively, one could lead theexhaust to the suction side of the turbo compressor prior to theintercooler, but this is not practical, since hot dirty exhaust wouldsoon destroy the intercooler.

The purpose of the present invention is, starting from a conventionalvalve mechanism of the type described by way of introduction, to achievean arrangement, by means of which exhaust can be returned to the intakeair without requiring an extra shutter and valve system on the exhaustand intake side.

This is achieved according to the invention by means of a valvemechanism which has transmission means which are arranged to selectivelyopen the exhaust valve during the engine intake stroke to draw exhaustinto the cylinder during the intake stroke.

Such an arrangement avoids condicting the exhaust to the intake side andeliminates problems with soiling and deposits. The invention utilizesthe fact that, even in a supercharged engine, the pressure in thecylinder after the initial intake stroke during the intake cycle, islower than the exhaust pressure, due to the pressure drop over theintake valve. This eliminates the need for an extra pumping device forexhaust return.

According to a preferred embodiment of the valve mechanism according tothe invention, the transmission means comprise a second shaft rotatablyjournalled parallel to the rocker arm shaft and having first and secondpivot arms, non-rotatably joined to said shaft, the first of whichinteracts with the intake rocker arm to convert its rocking motion to arotary movement of the second shaft, and the second of which interactswith the exhaust rocker aim to convert the rotary movement of the secondshaft into a rocking movement of the exhaust rocker arm. One of saidsurfaces is made as a cam surface, so that the lifting of the exhaustvalve during the intake stroke is variable from no lift at all in apredetermined axial position of the second shaft to maximum lift after acertain displacement of the second shaft from said predeterminedposition.

By varying the length of the open time for the exhaust valve during theintake stroke it is possible to regulate the mount of recirculatedexhaust and determine the percentage of exhaust in the Combustion air.Since the opening of the exhaust valve is effected individually in eachcylinder and can be rapidly controlled, the mixing-in of exhaust will bewell defined and can be varied as a function of engine work load or rpmfor example. It is not affected by residual gases in the intake manifoldfor example as in conventional systems. Each axial position of thesecond shaft and thus of the second pivot arm will thus define a givenlifting height and time period of the exhaust valve during the intakestroke.

The invention will be described in more detail with reference toexamples shown in the accompanying drawings, where

FIG. 1 is a schematic perspective view of one embodiment of a valvemechanism according to the invention,

FIG. 2 is a side view of an intake rocker arm with associated drivemeans,

FIG. 3 is a side view of an exhaust rocker arm with associated drivemeans,

FIG. 4 is a plan view of a detail in FIGS. 2 and 3,

FIG. 5 is a pressure and valve lift diagram,

FIG. 6 is a schematical longitudinal section of a cylinder chamber withpiston and valves, and

FIG. 7 is a schematic plan view of a valve mechanism for a six cylinderengine with a schematically represented control system.

In FIG. 1, the numeral 1 designates a rocker arm shaft, on which thereare journalled a rocker arm 2 for an intake valve 3 and a rocker arm 4for an exhaust valve 5. Furthermore, a rocker arm 6 for a so-called unitinjector 7 is journalled on the rocker arm shaft 1.

Each rocker arm 2, 4 and 5 has an individual cam roller 8, 9 and 10,respectively, following; cams 11, 12 and 13, respectively, on the camshaft 14.

According to the invention, a second 15 is rotatably journalled parallelto the rocker arm shaft 1 in bearings 16 (see FIG. 7). The shaft 15 isalso axially displaceably mounted, as will be described in more detailbelow with reference to FIG. 7. A first pivot arm 17 and a second pivotarm 18 are fixed to the shaft 15. The pivot arm 17 has a rotatablyjournalled roller 19 which is in contact with the cam roller 8 of theintake rocker arm 2. The roller 19 is narrower than the roller 8 so thatit can be displaced axially while retaining contact with the roller 8when the shaft 15 is displaced axially. With the arrangement describedabove, the rocking movement of the intake rocker arm 2 is converted intoa reciprocating rotary movement of the shaft 15. The second pivot arm 18has an inclined cam surface 20, the highest and lowest points thereofare illustrated by the lines 20a and 20b, respectively in FIG. 3. Thecam surface 20 faces an opposing surface 21 on a pair of fingers 22 (canbe a single component) at one end of the exhaust rocker arm 4. Dependingon the axial setting of the shaft 15, the rocker arm 18, upon rotationof the shaft 15 will rock the exhaust rocker arm 4 and lift the exhaustvalve 5 from its seat when the cam surface 20 makes contact with thesurface 21 on the exhaust rocker arm 4.

In an axial limit position of the shaft 15, there will be no contactbetween the cam surface 20 and the surface 21 of the exhaust rocker arm4, and this means that the exhaust valve 5 will remain completely closedduring the intake stroke. In the other limit position, an outer portionof the surface 21 will be in contact with the highest point 20a of thecam surface 20, meaning that the exhaust valve 5 will be openedmaximally during the intake stroke. In a practical embodiment in anengine in which the maximum lift of the exhaust valve during the exhauststroke is approximately 13 mm, the maximum lift in the intake stroke canbe about 4 mm. In the diagram in FIG. 6, the curve P illustrates thepressure in the cylinder during compression and expansion. The curve Aillustrates the lifting movement of the exhaust valve 5 during theexhaust stroke and the curve 5 illustrates the lifting movement of theintake valve 3 during the intake stroke. The lifting movement of theexhaust valve 5 during the intake stroke is illustrated by the curvesEGR, where the uppermost curve illustrates the maximum lift and theunderlying curves randomly chosen lower valve Lifts. In practice, thecontrol of the exhaust return is continuously variable between zeroexhaust valve lift and maximum exhaust valve lift. As is also evidentfrom the diagram, the exhaust and intake valves 5 and 3, respectively,are synchronized during the intake stroke, so that the maximum liftheight is reached simultaneously.

FIG. 6 illustrates schematically a cylinder 30, the piston 31 of whichlies midway between upper and lower dead centres during the intakestroke. The intake valve 3 and the exhaust valve 5 are lifted maximally.When there is a charge pressure in the intake valve 32 of circa 1.6 barthere will be an exhaust pressure in the exhaust manifold 33 of circa1.4 bar. The pressure drop over the intake valve 3 due to the throttlingeffect will result in pressure in the cylinder 30 of about 1 bar, whichwill mean that exhaust will be drawn into the cylinder at the same timeas the intake air.

The valve mechanism according to the invention has been described in thepreceding structurally and functionally with reference to a singlecylinder. A multi-cylinder engine has interconnected transmission meanscorresponding to the number of cylinders which arc of the typedescribed, as is illustrated schematically in FIG. 7 for a six-cylinderengine. The shaft 15 in this case consists of six shaft components 15acoupled together, of which one is shown in FIG. 4. It consists of aU-shaped central portion 40, from which two shaft extensions 41 an 42extend. The shaft extension 41 has a central bore 43, the length andinner diameter of which correspond to the length and outer diameter ofthe shaft extension 42. The shaft extension 42 of a shaft component 15aextends into the bore 43 in the adjacent shaft component 15a, so that ashaft 15 is formed in the six-cylinder example shown, which consists ofsix shaft components 15a axially fixed relative to each other but freelyrotatable relative to each other.

In an alternative embodiment (not shown), the individual shaftcomponents 15a are fixed on a torsion rod which can be an axiallyslotted pipe.

Each shaft component 15a has a long lateral projection forming the firstpivot arm 17 and having a roller 19 journalled on a pin 19a and a shortlateral projection forming a second pivot arm 18 with a cam surface 20.Each shaft component 15a is provided with a central lubricant conduit44, so that a complete conduit is formed from one end to the other ofthe composite shaft 15.

FIG. 7 shows the composite shaft 15 and a control system for axialdisplacement of the same. The cam surfaces 20 are, for the sake ofillustration, turned 90° here relative to the position in reality. Theshaft 15 is biassed to the left in FIG. 7 by a spring 15 towards a limitposition in which no exhaust is returned by virtue of the fact that thecam surface 20 will assume a position in which it does not reach thesurface 21 of the exhaust rocker arm 4. The left-hand end of the shaft15 forms a piston 51 in a hydraulic cylinder 52. The pressure in thecylinder 52 determines the axial setting of the shaft 15 and thispressure is regulated by the engine central control unit 53 into whichrpm, load, temperature, etc, readings are fed, as indicated by thearrows 54, 55, 56. The control unit 53 controls a regulating valve 57and is programmed with the desired exhaust recirculation value as afunction of engine rpm and load, or engine temperature. The commandvalue for the axial position is compared with the actual value from aninductive positional sensor 58 on the shaft 15 and the control unit 53gives a signal dependent on the obtained values to the regulating valveto regulate the pressure in the cylinder 51 so that the shaft 15 ismoved to a position providing the desired exhaust recycling.

The arrangement according to the invention is extremely reliable due tothe fact that it uses known engine components in a known environment. Nopump or throttle is required in the exhaust system. It provides a welldefined mixing-in of exhaust in the intake air. The mixing-in can bevaried rapidly without delay and without any substantial differencesbetween the cylinders. Pre-programming of the engine control unit willmake possible simple control of the mixing-in within the entire workrange of the engine regardless of other parameters. The cost will be lowcompared to a conventional system with corresponding regulatingcapacity.

I claim:
 1. Valve mechanism in an internal combustion engine, comprisingat least one intake valve and at least one exhaust valve in eachcylinder, and for each cylinder at least two rocker arms journalled on arocker arm shaft for operating a respective one of said valves,characterized by transmission means (15,17,18), which is arranged toselectively move the exhaust valve (5) from a closed position toward anopen position during the engine intake stroke to draw exhaust into thecylinder (30) during the intake stroke.
 2. Valve mechanism according toclaim 1, characterized in that the transmission means comprises means(21) for varying the opening time of the exhaust valve (5) and the valvelift thereof.
 3. Valve mechanism according to claim 2, characterized inthat the transmission means (15,17,18) is synchronized with the rockermeans (2) of the intake valve (3), so that the set maximum valve lift ofthe exhaust valve (5) coincides with the maximum valve lift of theintake valve.
 4. Valve mechanism according to claim 1, characterized inthat the transmission means comprises elements (15,17,18) interactingwith the rocker arms (2,4) of the intake valve and the exhaust valve,said elements enabling a portion of the rocking movement of the intakerocker arm (2) to be transmitted to the exhaust rocker arm (4).
 5. Valvemechanism according to claim 4, characterized in that said elementscomprise a second shaft (15) rotatably journalled parallel to the rockerarm shaft (1) and having first and second pivot arms (17,18),non-rotatably joined to said second shaft, the first pivot arm (17)interacts with the intake rocker arm (2) to convert its rocking movementinto a rotary movement of the second shaft (15) and the second pivot arm(18) interacts with the exhaust rocker arm (4) to convert the rotarymovement of the second shaft into a rocking movement of the exhaustrocker arm.
 6. Valve mechanism according to claim 5, characterized inthat the first pivot arm (17) at a distal end has a roller (19) incontact with a cam roller (8) on the intake rocker (2).
 7. Valvemechanism according to claim 5, characterized in that the second shaft(15) is axially displaceable, that the second pivot arm (18) has asurface (20) facing a cooperating surface (21) on an end of the exhaustrocker arm (4) and that one of said surfaces (20,21) has a cam surfaceshaped so that the lift of the exhaust valve during the intake stroke isvariable from no lift, in a predetermined axial position of the secondshaft (15), to maximum lift at a certain displacement of the secondshaft from said predetermined position.
 8. Valve mechanism according toclaim 7, characterized in that the second shaft (15) is constantlybiased in a direction towards the predetermined position by a spring(50) and is displaced by pressure medium in an opposing direction, thata control unit (53) is arranged which regulates the pressure of themedium depending on values supplied to the control unit of at leastengine rpm and load and of the position of the second shaft sensed by apositional sensor (58).
 9. Valve mechanism according to claim 5,characterized in that the second shaft (15) in a multi-cylinder engineis divided into separate shaft components (15a ) for the individualcylinders, said shaft components being arranged for axial displacement,but which permit pivoting of the first and second pivot arms (17,18) foreach cylinder relative to the pivot arms for the other cylinders.